Evaluation of computerized edge tracking for quantifying intima-media thickness of the common carotid artery from B-mode ultrasound images.

A new method to measure carotid intima-media thickness (IMT) from B-mode ultrasound images was developed that utilizes automatic tracking of the lumen-intima and media-adventitia echoes. Phantom studies and human replicate studies under typical clinical protocols for common carotid IMT measurement were carried out to assist in evaluation of the method. A lucite step wedge phantom was used to show that incorporation of sub-pixel interpolation to locate echo boundaries allowed detection of changes in the echo separation that were 5-10 times smaller than the axial resolution of the ultrasound transducer. For average IMT measured in the distal common carotid artery (CCA) wall in 24 subjects scanned twice within 60 days, mean absolute difference was 0.036 mm with a standard deviation of 0.045 mm. Replicate scans obtained 1 week apart of eight subjects by three sonographers showed the intersonographer variability was 5.4%. In another study of 12 subjects scanned every 4 months for 48 months, the root mean square deviation of the IMT measurements from a linear regression line was 0.030 mm. These data indicate that the method is equally precise over short intervals (60 days) and over long intervals (48 months). The new automated computerized edge tracking method presented in this paper represents an advance for image analysis of B-mode ultrasound images of common carotid IMT with measurement variability substantially reduced (2 to 4 times) compared with currently available manual methods.